In a lithium ion secondary battery using a Sn alloy as an active material for a negative electrode, the Sn alloy repeatedly expands and contracts caused by repeated charge and discharge. This repeated expansion and contraction results in the problem that the cycle properties of the lithium ion secondary battery worsen.
Patent Document 1 discloses a negative electrode material for a nonaqueous electrolyte secondary battery containing an intermetallic compound based on Co, Sn, and the like and a method for the manufacture thereof. Patent Document 2 discloses a negative electrode material for a nonaqueous electrolyte secondary battery using Co, Sn, and Ti and a method for the manufacture thereof in which an alloy material A which is a mixture of intermetallic compounds based on CoSn and CoSn2 and an alloy material B which is an intermetallic compound of the formula: CoxTiySn are separately prepared by the rapid solidification process and these two materials are mixed in a predetermined proportion. That document states that by so doing, it is possible to suppress precipitation of a Sn phase and to improve the cycle properties of a nonaqueous electrolyte secondary battery.